198 F. B. TAYLOR ORIGIN OF THE EARTH^S PLAN 



The crustal sheet or "plate/^ as Suess calls it, lying north and north- 

 west of the European Tertiar}- ranges, was quite small as compared with 

 that wJiich lay to the north of the Himalaya and t]ie Malay and Iranian 

 earth-lobes, and it was the magnitude or mass of this ^^plate" which in eacli 

 case determined the power of the crustal advance and probably also the 

 horizontal distance of the advance. In Asia the Tertiary advance closed 

 and completely overwhelmed the ancient greater Mediterranean Sea, the 

 Tethys of Suess, whereas in Europe the same movement fell far short of 

 this result and closed only a part of the sea, leaving the modern Mediter- 

 ranean in its present state. It can not be doubted that the southward 

 pressure of the creeping crust was far greater in Asia than in Europe. 

 Where the forward movement of the crust was more vigorous, as in Asia, 

 minor causes tending to interfere and produce irregularities were over- 

 whelmed; but in Europe, where the movement was relatively feeble, the 

 minor forces were favored and the impress of their action remains today. 



The thrust from the east, seen in the Eoumanian, Alpine, and Betic 

 arcs, appears to have been a deflected force arising probably from the re- 

 sistance of Indo-Africa to the southward crustal movement in Asia. 

 Although it produced locally a marked effect, it was apparently a rela- 

 tively feeble force. 



On general principles one is inclined to believe that forward over- 

 thrusts — that is, moving in the same direction as the general crustal 

 creep, like that at the base of the Himalaya — are likely to be of greater 

 extent than underthrusts which only produce the effect of overthrusts in 

 a backward or opposite direction. Agreeably with this idea, the great 

 overthrust to the east-southeast in Scandinavia has a length of nine de- 

 grees in latitude and a known width of over 100 kilometers. This is 

 much more extensive than any of the others in Europe, and the others 

 are all in the opposite direction. It seems probable, therefore, tliat the 

 Scandinavian case is a true forward overthrust, while the others in Eu- 

 rope are southward or southeastward underthrusts. This, of course, does 

 not take away the appearance of overthrusting in these latter cases, but 

 the tangential force which affected the mass above the thrust plane is in 

 such cases to be regarded as a reflex thrust force, directed backward over 

 the advancing undermass. The upper mass in a case of underthrust 

 might be descrilied as a backward overthrust in distinction from a for- 

 ward or true overthrust. 



The resistance of the African plateau may also have contributed some- 

 thing to the irregular forms in Europe, especially in favoring the per- 

 sistence of some of the Mediterranean basins, or possibly the making of 

 them. The Atlas Mountain ranges of Africa belong structurally to the 



